Stereoselective synthesis of chalcogen-tethered γ-lactams via 5-exo-dig cyclisation under visible-light irradiation

Abstract

We report a rapid, eco-friendly, and catalyst-free method for the stereoselective synthesis of chalcogen-tethered γ-lactams under visible-light irradiation. Using dimethyl carbonate as a green solvent, the reaction proceeds via 5-exo-dig intramolecular radical cyclization, affording Z-configured γ-lactams with high selectivity and broad substrate scope, including sulfur and selenium derivatives. The protocol is operationally simple, metal-free, and aligns with green chemistry principles. Notably, its translation to continuous-flow conditions using a K₃PO₄ glass-packed reactor significantly improved the reaction rate and yield, demonstrating excellent scalability. This approach offers a sustainable and efficient route to valuable chalcogenated γ-lactams, relevant to medicinal and synthetic chemistry.